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        <p>Library Version 11.2.5.3</p>
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          <th colspan="3" align="center">Opening a Transactional Environment and
            <span xmlns="http://www.w3.org/1999/xhtml">Database</span>
            
            
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          <td width="20%" align="left"><a accesskey="p" href="enabletxn.html">Prev</a> </td>
          <th width="60%" align="center">Chapter 2. Enabling Transactions</th>
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          <div>
            <h2 class="title" style="clear: both"><a id="envopen"></a>Opening a Transactional Environment and
            <span>Database</span>
            
            
        </h2>
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      <p>
            To enable transactions for your environment, you must initialize the
            transactional subsystem. Note that doing this also initializes the
            logging subsystem. In addition, you must initialize the memory pool
            (in-memory cache). You must also initialize the locking subsystem.  
            
            
            <span>
                For example:
            </span>
            
        </p>
      <p>
        Notice in the following example that you create your environment
        handle using the <code class="function">db_env_create()</code> function before you open 
        the environment:
    </p>
      <pre class="programlisting">#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;

#include "db.h"

int
main(void)
{
    int ret, ret_c;
    u_int32_t env_flags;
    DB_ENV *envp;
    const char *db_home_dir = "/tmp/myEnvironment";
    
    envp = NULL;

    /* Open the environment */
    ret = db_env_create(&amp;envp, 0);
    if (ret != 0) {
        fprintf(stderr, "Error creating environment handle: %s\n",
            db_strerror(ret));
        return (EXIT_FAILURE);
    }

    env_flags = DB_CREATE |    /* Create the environment if it does 
                                * not already exist. */
                DB_INIT_TXN  | /* Initialize transactions */
                DB_INIT_LOCK | /* Initialize locking. */
                DB_INIT_LOG  | /* Initialize logging */
                DB_INIT_MPOOL; /* Initialize the in-memory cache. */

    ret = envp-&gt;open(envp, db_home_dir, env_flags, 0);
    if (ret != 0) {
        fprintf(stderr, "Error opening environment: %s\n",
            db_strerror(ret));
        goto err;
    }

err:
    /* Close the environment */
    if (envp != NULL) {
        ret_c = envp-&gt;close(envp, 0);
        if (ret_c != 0) {
            fprintf(stderr, "environment close failed: %s\n",
                db_strerror(ret_c));
            ret = ret_c;
        }
    }

    return (ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE);
} </pre>
      <p>
        You then create and open your database(s) as you would for a non-transactional system.
        <span>
            The only difference is that you must pass the environment handle to
            the 
                <span>
                    <code class="function">db_create()</code> function, 
                </span>
                
             and you must open the database within a transaction.
             Typically auto commit is used for this purpose. To do so, pass 
            <code class="literal">DB_AUTO_COMMIT</code> to the database open command.
            It is recommended that you close all your databases before you close 
            your environment.
            For example:
        </span>

        
    </p>
      <pre class="programlisting">#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;

#include "db.h"

int
main(void)
{
    int ret, ret_c;
    u_int32_t <strong class="userinput"><code>db_flags,</code></strong> env_flags;
    <strong class="userinput"><code>DB *dbp;</code></strong>
    DB_ENV *envp;
    const char *db_home_dir = "/tmp/myEnvironment";
    <strong class="userinput"><code>const char *file_name = "mydb.db";
    
    dbp = NULL;</code></strong>
    envp = NULL;

    /* Open the environment */
    ret = db_env_create(&amp;envp, 0);
    if (ret != 0) {
        fprintf(stderr, "Error creating environment handle: %s\n",
            db_strerror(ret));
        return (EXIT_FAILURE);
    }

    env_flags = DB_CREATE |    /* Create the environment if it does 
                                * not already exist. */
                DB_INIT_TXN  | /* Initialize transactions */
                DB_INIT_LOCK | /* Initialize locking. */
                DB_INIT_LOG  | /* Initialize logging */
                DB_INIT_MPOOL; /* Initialize the in-memory cache. */

    ret = envp-&gt;open(envp, db_home_dir, env_flags, 0);
    if (ret != 0) {
        fprintf(stderr, "Error opening environment: %s\n",
            db_strerror(ret));
        goto err;
    }

    <strong class="userinput"><code>/* Initialize the DB handle */
    ret = db_create(&amp;dbp, envp, 0);
    if (ret != 0) {
        envp-&gt;err(envp, ret, "Database creation failed");
        goto err;
    }

    db_flags = DB_CREATE | DB_AUTO_COMMIT;
    ret = dbp-&gt;open(dbp,        /* Pointer to the database */
                    NULL,       /* Txn pointer */
                    file_name,  /* File name */
                    NULL,       /* Logical db name */
                    DB_BTREE,   /* Database type (using btree) */
                    db_flags,   /* Open flags */
                    0);         /* File mode. Using defaults */
    if (ret != 0) {
        envp-&gt;err(envp, ret, "Database '%s' open failed",
            file_name);
        goto err;
    }</code></strong>


err:
    <strong class="userinput"><code>/* Close the database */
    if (dbp != NULL) {
        ret_c = dbp-&gt;close(dbp, 0);
        if (ret_c != 0) {
            envp-&gt;err(envp, ret_c, "Database close failed.");
            ret = ret_c;
        }
    }</code></strong>


    /* Close the environment */
    if (envp != NULL) {
        ret_c = envp-&gt;close(envp, 0);
        if (ret_c != 0) {
            fprintf(stderr, "environment close failed: %s\n",
                db_strerror(ret_c));
            ret = ret_c;
        }
    }

    return (ret == 0 ? EXIT_SUCCESS : EXIT_FAILURE);
} </pre>
      <div class="note" style="margin-left: 0.5in; margin-right: 0.5in;">
        <h3 class="title">Note</h3>
        <p>
                Never close a database  that has active transactions. Make sure
            all transactions are resolved (either committed or aborted)
            before closing the database.
        </p>
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